Sandbox 14

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Trypsin


Trypsin is a serine protease responsible for the hydrolysis of proteins. This process is biologically applicable in the process of digestion. Unlike other studied proteins such as αLytic Protease and Streptomyces griseus, SGPB, trypsin exists in a thermodynamically stable state. Trypsin requires no pro region, like its counterparts αLP and SGPB, or its zymogen to fold. It was found that typsin had the same unfolding rate as αLP and SGPB. Truhlar et al have since postulated that the susceptibility of trypsin to inactivation is due to the fact that trypsin is less optimized in suppressing its unfolded state. This feature of trypsin serves as an advantage since ,unlike extracellular αLP and SGPB, trypsin is released inside the protein composed gut of mammals. Trypsin should therefore be able to easily alternate between its folded active state and unfolded inactivated state. Trypsin, like other serine proteases, is very specific in its reaction. It cleaves at peptide bonds located after residues with positive side chains, namely, arginine and lysine.

Catalytic triad
T The active site of trypsin is a catalytic triad with residues His57,Asp102 and Ser 195. They are linked in the sequence Asp102---His57---Ser195. Each of these residues have a specific role to play in the hydrolysis of peptide bonds. These groups are held together by hydrogen bond interactions. Ser 195 is responsible for the attack of the carbonyl groups of the peptide bond to be hydrolyzed. It does this using the oxygen of its hydroxide group and in the process transfers a proton to His57. It leaves the attacked carbonyl group with a tetrahedral structure and a negatively charged oxygen (the negatively charged oxygen is stabilized by an oxyanion hole formed by the backbone of Gly 193 and Ser 195 within the protein). The negatively charged tetrahedral intermediate collapse to form an acyl-enzyme complex. This step is aided by the transfer of protons from the amino acid group, histidine (His 57) to the amino group of the substrate. The amino group is then free to depart. Water hydrolyses the bond between the carbonyl group of the substrate and the oxygen of Ser 195. The substrate is cleaved and the catalytic triad is regenerated. In this process Asp102 has been found to stabilize the charge formed on the protonated His 57. This process of peptide bond hydrolysis is generally divided into two steps: the first one is the acylation of the enzyme and the second, the deacylation and consequent regeneration of the enzyme.

The mechanism outlined for the hydrolysis of peptide bonds, including the presence of the catalytic triad, is applicable to both bovine and rat trypsin.

Effects of Glycine on Stability




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